diff --git a/Zend/zend_ast.c b/Zend/zend_ast.c
index 2e4edeee5d98b..5edd4c4d37ed6 100644
--- a/Zend/zend_ast.c
+++ b/Zend/zend_ast.c
@@ -769,12 +769,6 @@ static zend_result ZEND_FASTCALL zend_ast_evaluate_ex(zval *result, zend_ast *as
 			break;
 		case ZEND_AST_CONST_ENUM_INIT:
 		{
-			// Preloading will attempt to resolve constants but objects can't be stored in shm
-			// Aborting here to store the const AST instead
-			if (CG(in_compilation)) {
-				return FAILURE;
-			}
-
 			zend_ast *class_name_ast = ast->child[0];
 			zend_string *class_name = zend_ast_get_str(class_name_ast);
 
@@ -792,6 +786,12 @@ static zend_result ZEND_FASTCALL zend_ast_evaluate_ex(zval *result, zend_ast *as
 			}
 
 			zend_class_entry *ce = zend_lookup_class(class_name);
+			if (!ce) {
+				/* Class may not be available when resolving constants on a dynamically
+				 * declared enum during preloading. */
+				ZEND_ASSERT(CG(compiler_options) & ZEND_COMPILE_PRELOAD);
+				return FAILURE;
+			}
 			zend_enum_new(result, ce, case_name, case_value_ast != NULL ? &case_value_zv : NULL);
 			zval_ptr_dtor_nogc(&case_value_zv);
 			break;
diff --git a/ext/opcache/ZendAccelerator.c b/ext/opcache/ZendAccelerator.c
index 9bcd035c35295..2d0586ccef875 100644
--- a/ext/opcache/ZendAccelerator.c
+++ b/ext/opcache/ZendAccelerator.c
@@ -3755,6 +3755,19 @@ static zend_result preload_resolve_deps(preload_error *error, const zend_class_e
 	return SUCCESS;
 }
 
+static zend_result preload_update_constant(zval *val, zend_class_entry *scope)
+{
+	zval tmp;
+	ZVAL_COPY(&tmp, val);
+	if (zval_update_constant_ex(&tmp, scope) == FAILURE || Z_COLLECTABLE(tmp)) {
+		zval_ptr_dtor(&tmp);
+		return FAILURE;
+	}
+	zval_ptr_dtor_nogc(val);
+	ZVAL_COPY_VALUE(val, &tmp);
+	return SUCCESS;
+}
+
 static bool preload_try_resolve_constants(zend_class_entry *ce)
 {
 	bool ok, changed, was_changed = false;
@@ -3768,7 +3781,7 @@ static bool preload_try_resolve_constants(zend_class_entry *ce)
 		ZEND_HASH_MAP_FOREACH_PTR(&ce->constants_table, c) {
 			val = &c->value;
 			if (Z_TYPE_P(val) == IS_CONSTANT_AST) {
-				if (EXPECTED(zval_update_constant_ex(val, c->ce) == SUCCESS)) {
+				if (EXPECTED(preload_update_constant(val, c->ce) == SUCCESS)) {
 					was_changed = changed = true;
 				} else {
 					ok = false;
@@ -3786,7 +3799,7 @@ static bool preload_try_resolve_constants(zend_class_entry *ce)
 				val = &ce->default_properties_table[i];
 				if (Z_TYPE_P(val) == IS_CONSTANT_AST) {
 					zend_property_info *prop = ce->properties_info_table[i];
-					if (UNEXPECTED(zval_update_constant_ex(val, prop->ce) != SUCCESS)) {
+					if (UNEXPECTED(preload_update_constant(val, prop->ce) != SUCCESS)) {
 						resolved = ok = false;
 					}
 				}
@@ -3802,7 +3815,7 @@ static bool preload_try_resolve_constants(zend_class_entry *ce)
 			val = ce->default_static_members_table + ce->default_static_members_count - 1;
 			while (count) {
 				if (Z_TYPE_P(val) == IS_CONSTANT_AST) {
-					if (UNEXPECTED(zval_update_constant_ex(val, ce) != SUCCESS)) {
+					if (UNEXPECTED(preload_update_constant(val, ce) != SUCCESS)) {
 						resolved = ok = false;
 					}
 				}
diff --git a/ext/zend_test/tests/gh13970.phpt b/ext/zend_test/tests/gh13970.phpt
new file mode 100644
index 0000000000000..8a52f3f47c8c2
--- /dev/null
+++ b/ext/zend_test/tests/gh13970.phpt
@@ -0,0 +1,21 @@
+--TEST--
+GH-13970 (Incorrect validation of #[\Attribute]’s first parameter)
+--EXTENSIONS--
+zend_test
+--FILE--
+<?php
+#[Attribute(\ZendTestUnitEnum::Foo)]
+class Foo {
+
+}
+
+#[Foo]
+function test1() {
+
+}
+
+$reflection = new ReflectionFunction('test1');
+var_dump($reflection->getAttributes()[0]->newInstance());
+?>
+--EXPECTF--
+Fatal error: Attribute::__construct(): Argument #1 ($flags) must be of type int, ZendTestUnitEnum given in %s on line %d